1. Technical Field
The present invention generally relates to internal combustion engines. More particularly, the invention relates to a method and system for diagnosing engines based on a single in-cylinder pressure measurement.
2. Discussion
Modern day engine diagnosis is typically quite complex and involves evaluating numerous systems such as valve trains, ignition systems, air intake systems, exhaust systems, emission control systems, and combustion systems. The typical automotive combustion system uses internal combustion to convert fuel into motion. In fact, almost all vehicles currently use what is called a four-stroke combustion cycle made up of an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke. Under such a system, a piston is connected to a crankshaft by a connecting rod. During the intake stroke, one or more intake valves open and the piston increases the internal volume of the combustion cylinder while taking in a cylinder-full of air and gasoline (i.e., the fuel mixture). The compression stroke occurs when the piston reduces the volume of the cylinder thereby compressing the fuel mixture. When the compression stroke is complete (e.g., at top dead center), the combustion stroke begins and a spark plug emits a spark to ignite the gasoline. The compressed fuel mixture in the cylinder explodes, driving the piston down and increasing the volume of the cylinder. Since the piston is connected to the crankshaft, this combustion translates into rotational energy that is transferred to the wheels of the vehicle. Once the piston hits the bottom of its stroke, the exhaust stroke begins by opening one or more exhaust valves and allowing the exhaust to leave the cylinder and exit the vehicle through the tail pipe.
While much time and effort has been spent on evaluating the above-described combustion cycle, certain difficulties remain. For example, the conventional approach involves measuring the rotational speed of the crankshaft (i.e., the engine speed), measuring the vehicle speed, and drawing combustion inferences based on these measurements. For example, if it is determined that the engine speed is abnormally low in relation to the measured vehicle speed, combustion problems may exist. It is important to note, however, that such an approach can be inaccurate and may lead to incorrect misfiring determinations. It is therefore desirable to provide an approach to engine diagnosis that enables more accurate determinations of combustion quality.
In recent years, attempts have been made at directly measuring the in-cylinder pressure during the combustion cycle and using these measurements to determine combustion quality. This approach, however, typically requires numerous measurements to be made throughout the combustion cycle and therefore involves a significant amount of processing overhead and cost. For example, one measurement system collects as many as 720 in-cylinder measurements during a single combustion cycle. Thus, while in-cylinder pressure measurements are generally more accurate than the above-described conventional approach, production volume implementation is impractical. It is therefore desirable to provide an approach to generating a combustion quality calculation that is both accurate and does not require a significant amount of processing overhead.
The above and other objectives are provided by an engine combustion diagnostic system and method for diagnosing an engine in accordance with the principles of the present invention. The method includes the step of linking manifold absolute pressure (MAP) to in-cylinder pressure during calibration of the engine such that a table results. A single in-cylinder pressure measurement is collected during real-time operation of the engine. The method further provides for determining combustion quality for the engine based on the real-time in-cylinder pressure measurement and the table. By limiting data collection to a single in-cylinder pressure measurement, the method significantly improves accuracy while maintaining processing overhead at a reasonable level.
Further in accordance with the invention, a method for determining combustion quality for an engine is provided. The method includes the step of determining a real-time ratio based on a real-time in-cylinder pressure measurement and a real-time MAP measurement. The real-time MAP measurement is matched to an entry in a table having a calibration MAP measurement that is approximately equal to the real-time MAP measurement. The method further provides for dividing the real-time ratio by a calibration ratio corresponding to the entry. The calibration ratio is based on a calibration in-cylinder pressure measurement and the calibration MAP measurement such that a combustion quality calculation results.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute part of this specification. The drawings illustrate various features and embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.